Effect of Hydrocarbon on DeNOx Performance of Selective Catalytic Reduction by a Combined Reductant over Cu-Containing Zeolite Catalysts

The effects of hydrocarbons (HCs) on a combined selective catalytic reduction (SCR) system by NH₃ and mixed HCs for simulated exhaust over five different types of Cu²⁺-exchanged zeolite catalysts have been systematically examined according to the reaction temperature. CuSSZ-13 with three-dimensional (3D) small pores and CuFER with 2D medium- A nd small-pore channels showed good resistance to poisoning by heavy HCs such as dodecane (C₁₂H₂₆) and m-xylene (C₈H₁₀), while they were not tolerant to poisoning by short-chain HCs such as propylene (C₃H₆). The deNOx activities of CuZSM-5 and CuBEA containing 3D medium- A nd large-pore channels, respectively, were significantly decreased by the inclusion of C₁₂H₂₆ in the reaction feed stream. Another large-pore channel-based zeolite catalyst, CuMOR, showed a peculiar behavior of NOx reduction by the combined SCR: Complete conversions of NO and NH₃ without any side reactions in the medium-temperature region, probably due to small-pore side pockets alongside straight large-pore channels. The NH₃/SCR performances of the catalysts tested varied depending on the structural features of the zeolite supports, while there were somewhat common features according to the reaction temperatures. Inhibition of surface NO oxidation by adsorbed HCs was the primary cause of the decrease in NH₃/SCR performance at low temperature. In the medium-temperature region, NH₃ reacted with HCs to form nitrile compounds through ammoxidation, resulting in a further decrease in deNOx activity due to a shortage of NH₃ for NOx reduction. On the other hand, deNOx activity increased at high temperature due to NOx reduction by HCs present in the feed stream.